Electrical lighting has become commonplace in modern society. Electrical lighting devices are commonly deployed, for example, in homes, buildings of commercial and other enterprise establishments, as well as in various outdoor settings. With the advent of modern electronics has come advancement both in the types of light sources and in the control capabilities within the lighting devices. For example, solid state sources are now becoming a commercially viable alternative to traditional light sources such as incandescent and fluorescent lamps. By nature, solid state light sources such as light emitting diodes (LEDs) are easily controlled by electronic logic circuits or processors.
The last decade or so has also seen an explosion of demand for data communication services; and increasingly, this demand include demand for wireless connectivity. Cellular and WiFi services are now quite common. However, there have also been proposals to use light-based communication technologies as an alternative to radio-frequency (RF) based wireless communications. Light wave communications, for example, do not interfere with existing RF are not currently subject to regulation or license requirements. Hence, along with the transition to solid state light sources has come an increased interest in using light as an over-the-air mechanism to transport data.
Visual Light Communication (VLC) therefore will likely become a very popular piece of the hybrid network (to increase bandwidth optimization in wireless communication systems). In many cases, the output of a lighting device deployed for a normal lighting purpose, e.g. general white light illumination, is modulated in a manner not readily perceptible by human occupants in the illuminated space but so that the modulated light carries transmitted data.
Traditionally, a switching FET is used either in series or parallel with the LEDs to provide dimming (usually pulse width modulation (PWM)) and high speed switching for VLC to implement the modulation. Those methods tend to be lossy because power is wasted in the FET and almost always requires some storage mechanism in parallel with the load. In another method, the power supply (or LED driver) itself is turned ON and OFF to provide dimming and VLC. In any of these methods, the ‘data’ signal is added onto the dimming signal. There are limitations with all of these approach since two types of switching cycles have to be super-imposed. One switching cycle is the cycle of the switcher itself, which provides the requisite current regulation; and the other switching cycle is the cycle of ‘dimming module,’ which requires additional control of LED switching. This can be costly, can be cumbersome, and potentially may create Electromagnetic interference (EMI) issues. These limitations tend to limit the switching speed available for carrying data and result in relative low data transmission rates.
There is still room for further improvement in the technologies used for VLC or other similar types of light-based data communications.